Process for producing single crystal of compound semiconductor and crystal growing apparatus

ABSTRACT

In a production method for producing a compound semiconductor single crystal by LEC method using a crystal growth apparatus with a double crucible structure, it was made to grow up a crystal by covering the second crucible with a plate-like member having a pass-through slot for being capable of introducing a crystal pulling-up shaft having a seed crystal holding part at a tip into the second crucible and creating a state where an atmosphere within the second crucible scarcely changes (a semi-sealed structure).

TECHNICAL FIELD

The present invention relates to a production method of a compoundsemiconductor single crystal and a crystal growth apparatus, inparticular, the present invention relates to a method for producing, forexample, a ZnTe-based compound semiconductor single crystal by a liquidencapsulated Czochralski (LEC) method, and a useful technique applicableto the crystal growth apparatus.

DESCRIPTION OF RELATED ART

At present, a ZnTe-based compound semiconductor single crystal isexpected as a crystal available for a pure green light-emitting device.Further, in recent years, devices for enhancing conductivity of thecrystal have been made in order to further improve light emissionproperties as a light-emitting device. As for a method thereof, a methodfor adding impurities such as phosphorus or arsenic in the crystal hasbeen carried out.

As for this method, there is used a growth method such as a verticalBridgman (VB) method or a vertical gradient freezing (VGF) method, inwhich impurities can be added during the crystal growth.

However, in the production of the ZnTe-based compound semiconductorsingle crystal according to the VB method or the VGF method, alarge-sized crystal can be grown but on the contrary, there often arisesa problem that the crystal is cracked due to a difference in thermalexpansion between an encapsulating material and a grown crystal becausethe crystal is grown by the cooling in a state of being covered with theencapsulating material.

Consequently, the present inventors have proposed a technique of growinga large-sized ZnTe-based compound semiconductor single crystal utilizinga liquid encapsulated Czochralski method (LEC method) in whichimpurities can be added during the crystal growth in the same manner asin the VB method or the VGF method (Japanese Patent ApplicationPublication-Tokugan-2002-249963).

The above-described prior application technique is a technique ofgrowing a crystal by the LEC method using a crystal growth apparatuswith a double crucible structure, in which the crystal is grown whilekeeping a state where a surface of the grown crystal is covered with anencapsulating material until the crystal growth is completed, wherebyevaporation of the constituent components from the surface of the growncrystal can be suppressed and deterioration in crystallinity of thegrown crystal can be prevented, so that a single crystal havingexcellent quality can be grown.

Incidentally, in the prior application technique, the crystal is grownalong an inner wall of the inner crucible, whereby the surface of thegrown crystal can be covered with an encapsulating material until thecompletion of the crystal growth without using a large amount of theencapsulating material.

However, even if the surface of the grown crystal is covered with anencapsulating material, the constituent components of the grown crystalcannot be sufficiently prevented from being decomposed and theconstituent components of the grown crystal may be evaporated.

Accordingly, the present invention is a technique applicable to thecrystal growth method utilizing the LEC method, and the object of thepresent invention is to provide a production method of a compoundsemiconductor single crystal and a crystal growth apparatus, in whichevaporation of the constituent components of the grown crystal can beeasily prevented to grow a large-sized ZnTe-based compound semiconductorsingle crystal having excellent crystal quality.

DISCLOSURE OF INVENTION

In order to attain the above purpose of the invention,

-   -   a production method for producing a compound semiconductor        single crystal, comprises: housing semiconductor raw materials        and an encapsulating material in a raw material melt housing        part composed of a bottomed cylindrical-shaped first crucible        and a second crucible having a communicating opening with the        first crucible at a bottom in a state of being disposed within        the first crucible; covering the second crucible with a        plate-like member to have provided a pass-through slot of        enabling the introduction of a crystal pulling-up shaft having a        seed crystal holding part at the end into the second crucible so        as to create a state where an atmosphere within the second        crucible scarcely changes; heating the raw material housing part        to melt the raw materials and lowering the crystal pulling-up        shaft to bring a seed crystal into contact with the surface of        the raw material melt; and growing a crystal while raising the        crystal pulling-up shaft (the so-called LEC method).

Herein, a state where an atmosphere within the second crucible scarcelychanges is a state where the crucible is completely sealed or isconsidered to be almost sealed although a slight space is left, and itmeans a state where the constituent components in the atmosphere or avapor pressure thereof scarcely changes.

According to this construction, the grown crystal is pulled up withinthe second crucible and the surface of the crystal is exposed from theencapsulating material along with the progress of the growth, however,the inside of the second crucible has an almost sealed structure, sothat evaporation of the constituent components from the surface of thegrown crystal can be effectively suppressed. Therefore, a high-qualitycompound semiconductor single crystal having no decomposition on thecrystal surface can be produced. Further, impurities can be easily addedduring the crystal growth by use of the LEC method, so that asemiconductor device such as a light-emitting device having desiredproperties can be produced using a produced single crystal as a basebody.

Incidentally, even in the general LEC method where a surface of thegrown crystal is exposed from an encapsulating material along with thepulling-up of the grown crystal, evaporation of the constituentcomponents of the grown crystal can be suppressed, so that ahigh-quality single crystal reduced in crystal defects can be produced.

Further, the plate-like member is fixed to the crystal pulling-up shaftso as not to slip off in a state of being inserted by the crystalpulling-up shaft, and is supported at the top end of the side wall ofthe second crucible to work out to a cover when the crystal pulling-upshaft is lowered.

According to this construction, the crystal pulling-up shaft can besurely and easily introduced into the second crucible through theplate-like member and moreover, the grown crystal can be easily takenout from the second crucible.

As another method, there is also considered, for example, a method wherea plate-like member having provided thereon a pass-through slot ispreviously fixed on the upper part of the second crucible as a cover anda crystal pulling-up shaft is lowered from above the plate-like memberso as to be introduced into the second crucible through the pass-throughslot. However, according to the method, there is a possibility thatunless the center of the pass-through slot and that of the crystalpulling-up shaft coincide with an appreciable accuracy, the crystalpulling-up shaft collides with the plate-like member, as a result, bothare damaged. Further, it is also considered to increase the differencebetween the diameter of the pass-through slot and that of the crystalpulling-up shaft in anticipation of the deviation between the center ofthe pass-through slot and that of the crystal pulling-up shaft, however,there is a possibility that since the structure within the secondcrucible is widely different from the sealed structure, the constituentcomponents of the grown crystal evaporates. Further, when a cover isfixed on the second crucible, the cover must be removed in taking outthe grown crystal, which leads to reduction in productivity of thesingle crystal.

According to the present invention, there is no worry that such aproblem arises and the second crucible can be easily allowed to have asemi-sealed structure. Further, along with the rise of the crystalpulling-up shaft, the plate-like member is also directly removed fromthe inner crucible, so that the grown crystal can be easily taken out.

Further, a crystal growth apparatus of the invention comprises at least:an outer vessel which can be sealed; a bottomed cylindrical-shaped firstcrucible disposed within the outer vessel; a second crucible having acommunicating opening with the first crucible at the bottom in a stateof being disposed within the first crucible; a crystal pulling-up shafthaving a seed crystal holding part at the end; and a plate-like memberwhich has a pass-through slot of enabling the introduction of thecrystal pulling-up shaft into the second crucible and which works out toa cover of the second crucible.

According to such a crystal growth apparatus, the second crucible isalmost sealed during the crystal growth, so that constituent componentscan be effectively prevented from evaporating from the surface of thegrown crystal, as a result, a high-quality single crystal reduced incrystal defects can be produced.

Further, the plate-like member is previously inserted by the crystalpulling-up shaft which is provided with a slipping-off preventing memberto prevent the plate-like member from slipping off. For example, thefunction as the slipping-off preventing member can be made to use alsothe seed crystal holding part fixed to a tip of the crystal pulling-upshaft.

Further, it is preferable that the plate-like member is a quartz glassplate. According to this construction, a possibility that the quality ofthe grown crystal deteriorates due to evaporation of the constituentcomponents from the plate-like member decreases.

Further, by setting difference between the diameter of the pass-throughslot provided on the plate-like member and the diameter of the crystalpulling-up shaft to 1 mm or less, the inside of the second crucible canhave a semi-sealed structure effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic construction view of the crystal growth apparatusfor use in the embodiment of the present invention.

FIG. 2 is an explanatory view showing a growth process of a ZnTecompound semiconductor single crystal.

BEST MODE FOR CARRYING OUT THE INVENTION

The suitable embodiment of the present invention is described below byreferring to drawings.

FIG. 1 is a schematic construction view of the crystal growth apparatusaccording to the embodiment.

The crystal growth apparatus 100 of the embodiment is composed of ahigh-pressure vessel 1, a heat insulating material 2 and a heatingheater 3 disposed concentrically with the high-pressure vessel in theinside of the vessel, a rotation shaft 4 disposed vertically in thecentral part of the high pressure vessel 1, a susceptor 13 disposed atthe upper end of the rotation shaft 4, a bottomed cylindrical-shapedouter crucible (first crucible) 5 made of pBN and fitted into thesusceptor, an inner crucible (second crucible) 6 made of pBN anddisposed within the outer crucible 5, a rotary pulling-up shaft 7vertically provided above the inner crucible 6 and provided with a seedcrystal holder 8 fixing a seed crystal 9 at the lower end, and a quartzglass plate 10 inserted by the rotary pulling-up shaft 7 and held by theseed crystal holder 8 so as not to slip off.

The inner crucible 6 has a communicating opening 6 a which communicateswith the outer crucible 5 on the bottom surface so that a raw materialmelt 12 can move from the outer crucible 5 to the inner crucible 6through the communicating opening. In addition, the inner crucible 6 isfixed to the outer crucible 5 or other jigs by an appropriate holder(not shown).

Further, the rotary pulling-up shaft 7 is connected to a driving unit(not shown) disposed outside the high-pressure vessel 1 to construct arotary pulling-up mechanism. The rotation shaft 4 is connected to thedriving unit (not shown) disposed outside the high-pressure vessel 1 toconstruct a crucible rotating mechanism and a susceptor liftingmechanism. The rotation and lifting movement motions of the rotarypulling-up shaft 7 and the crucible rotation shaft 4 each independentlyis set and controlled.

Further, a pass-through slot having a diameter slightly larger than thatof the rotary pulling-up shaft 7 is provided in the center of the quartzglass plate 10 and the rotary pulling-up shaft 7 is inserted into thepass-through slot. It is desired, for example, that the differencebetween the diameter of the pass-through slot and that of the rotarypulling-up shaft 7 is adjusted to 1 mm or less. This is because when thediameter of the pass-through slot is made too large, a space between therotary pulling-up shaft 7 and the quartz glass plate 10 is increased, asa result, a function of sealing the inner crucible 6 is reduced.

Using the above-described crystal growth apparatus, a single crystal rodgrown from a seed crystal is pulled up with rotation so as to grow ahigh-purity single crystal at the lower end of the seed crystal by useof the liquid encapsulated Czochralski method.

Next, a method for producing a ZnTe compound semiconductor singlecrystal as one example of compound semiconductors by use of the crystalgrowth apparatus 100 is described in detail. FIG. 2 is an explanatoryview showing a growth process of the ZnTe compound semiconductor singlecrystal.

In the embodiment, a pBN crucible having a size of 100 mmφ in innerdiameter×100 mm in height×1 mm in thickness was employed as the outercrucible 5, and a pBN crucible having a size of 54 mmφ in innerdiameter×100 mm in height×1 mm in thickness was employed as the innercrucible 6. Further, a communicating opening 6 a having a diameter of 10mm is formed in the central part of the bottom surface of the innercrucible 6.

Further, a diameter of the rotary pulling-up shaft 7 was set to 12 mmφand a diameter of the pass-through slot provided on the quartz glassplate 10 was set to 13 mmφ.

First, into the outer crucible 5 and the inner crucible, Zn with apurity of 6N and Te with a purity of 6N as raw materials were put in anamount of 1.5 kg in total such that Zn and Te were in an equimolarratio, and the surface of the raw materials was covered with 400 g of anencapsulating material (B₂O₃) 11 so as to have an encapsulating materiallayer thickness of 35 mm.

Next, the outer crucible 5 and the inner crucible 6 were disposed on thesusceptor 13, and the inside of the high-pressure vessel 1 was filledwith an inactive gas (e.g., Ar) and adjusted so as to have apredetermined pressure. At this time, the inner crucible 6 was fixed bya holder so as to have a state where after the raw materials were meltedby use of the heating heater 2, the inner crucible was dipped in the rawmaterial melt in a depth of 20 mm from the liquid level.

Incidentally, the raw material melt was gradually decreased in quantityaccompanying the crystal growth, however, the susceptor 13 (outercrucible 5) was raised by the lifting drive of the rotation shaft 4 tocontrol a dipping state of the inner crucible 6. For example, the innercrucible 6 was held in a state of being dipped in the range of 10 mm to40 mm from the liquid level of the raw material melt.

Thereafter, while sealing the surface of the raw materials with theencapsulating material, the inner crucible was heated at a predeterminedtemperature using the heating heater 2 to melt Zn and Te for the directsynthesis and held for a given length of time in a state where the rawmaterials were melted.

Next, as shown in FIG. 2(a), the rotary pulling-up shaft 7 holding theseed crystal 9 was lowered. At this time, the quartz glass plate 10 islowered with the rotary pulling-up shaft because it is only supported bythe seed crystal holder 8. Herein, a ZnTe crystal having a crystalorientation of (100) was used as the seed crystal. Further, the seedcrystal was covered with a molybdenum cover (not shown) in order toprevent the seed crystal 9 from being decomposed.

Thereafter, as shown in FIG. 2(b), after the quartz glass plate 10reached a sidewall of the inner crucible 6, only the rotary pulling-upshaft 7 was introduced into the inner crucible 6 because the quartzglass plate 10 was supported by the inner crucible 6.

Subsequently, the seed crystal was brought into contact with the surfaceof the raw material melt and then, the rotary pulling-up shaft 7 wasrotated at a rotational speed of 1 to 2 rpm to form a shoulder part ofthe crystal while pulling up the crystal at a speed of 2.5 mm/h.Further, after the shoulder part of the crystal was formed, the cruciblerotation shaft was rotated at a rotational speed of 1 to 5 rpm to form abody part of the crystal while pulling up the crystal at a speed of 2.5mm/h. At this time, the diameter of the body part in the grown crystal10 was almost the same as the inner diameter of the inner crucible 6 asshown in FIG. 2(c), so that a crystal having a desired diameter could beeasily obtained without performing a precise diameter control accordingto the pulling-up speed and the rotational speed of the crucible or thepulling-up shaft.

After the completion of crystal growth, the crystal was cooled only fora predetermined time. Thereafter, the rotary pulling-up shaft 7 wasraised to take out a grown crystal as shown in FIG. 2(d). At this time,the quarts glass plate 10 was raised with the support by the seedcrystal holder 8, so that the grown crystal could be easily taken out.

As described above, the crystal growth according to the liquidencapsulated Czochralski method was performed and after the completionof the crystal growth, the grown crystal 10 was separated from theencapsulating material 11 to obtain a ZnTe compound semiconductorcrystal having no crack. The obtained ZnTe compound semiconductorcrystal had a glossy surface without having such surface decompositionthat was found in a crystal grown by a usual LEC method. This is becausethe inner crucible 6 was sealed by the quartz glass plate 10 andtherefore, the state of the atmosphere within the crucible scarcelychanged, so that the decomposition and evaporation of the grown crystalcould be prevented.

Further, the grown crystal had a size of 54 mmφ in diameter×60 mm inlength, so that a large-sized ZnTe-based compound semiconductor singlecrystal conventionally regarded as difficult could be realized.

The invention carried out by the present inventors was described abovein detail on the basis of the embodiment, however, the present inventionis not limited to the embodiment.

For example, in the embodiment, the crystal was grown along the innerdiameter of the inner crucible 6 so as to have a state where the surfaceof the grown crystal was covered with the encapsulating material,however, the present invention can be applied also in a general LECmethod where the surface of the grown crystal is exposed from theencapsulating material with the pulling-up of the grown crystal, andevaporation of the constituent components of the grown crystal can besuppressed, so that a high-quality single crystal reduced in crystaldefects can be produced.

Further, by adding impurities as a dopant in the raw material melt,conductivity of the crystal can be easily controlled. At this time, adifference is produced between the concentration of impurities in theraw material melt within the outer crucible 5 and the concentration ofimpurities in the raw material melt within the inner crucible 6,however, by changing the size of the communicating opening of the secondcrucible, the inner diameter of the second crucible, the differencebetween the concentrations of impurities in the raw material melts iscontrolled, as a result, the concentration of impurities in the rawmaterial melt within the inner crucible 6 can be kept constant.

According to the present invention, semiconductor raw materials and anencapsulating material are housed in a raw material melt housing partcomposed of a bottomed cylindrical-shaped first crucible and a secondcrucible having a communicating opening with the first crucible at thebottom in a state of being disposed within the first crucible, thesecond crucible is covered with a plate-like member having providedthereon a pass-through slot of enabling the introduction of a crystalpulling-up shaft having a seed crystal holding part at the end into thesecond crucible so as to create a state where an atmosphere within thesecond crucible scarcely changes, the raw material housing part isheated to melt the raw materials and the crystal pulling-up shaft islowered to bring a seed crystal into contact with the surface of the rawmaterial melt, and a crystal is grown while raising the crystalpulling-up shaft, so that the inside of the second crucible where thecrystal growth is performed has a semi-sealed structure, as a result,the evaporation of the constituent components from the surface of thegrown crystal can be effectively suppressed.

Accordingly, when growing a crystal using the LEC method, a high-qualitysingle crystal reduced in crystal defects can be produced. Further,impurities can be easily added during the crystal growth by the LECmethod, so that a semiconductor device such as a light-emitting devicehaving desired properties can be produced using the produced singlecrystal.

INDUSTRIAL APPLICABILITY

The present invention is effective in producing not only a ZnTe compoundsemiconductor single crystal but also a ternary or more ZnTe-basedcompound semiconductor single crystal containing ZnTe or other compoundsemiconductor single crystals. By applying the present invention, alarge-sized and high-quality compound semiconductor single crystal canbe obtained.

1. A production method for producing a compound semiconductor singlecrystal, comprising: housing semiconductor raw materials and anencapsulating material in a raw material melt housing part comprising abottomed cylindrical-shaped first crucible and a second crucible havinga communicating opening with the first crucible at a bottom in a stateof being disposed within the first crucible; covering the secondcrucible with a plate-like member having a pass-through slot for beingcapable of introducing a crystal pulling-up shaft having a seed crystalholding part at an end thereof, into the second crucible so as to createa state where an atmosphere within the second crucible scarcely changes;heating the raw material housing part to melt the raw materials andlowering the crystal pulling-up shaft to bring a seed crystal intocontact with a surface of the raw material melt; and growing a crystalwhile the crystal pulling-up shaft is raised; wherein the plate-likemember is fixed to the crystal pulling-up shaft so as not to slip off ina state that the crystal pulling-up shaft is inserted, and theplate-like member functions as a cover by being supported at a top endof a side wall of the second crucible when the crystal pulling-up shaftis lowered.
 2. (cancelled)
 3. A crystal growth apparatus comprising: anouter vessel which is sealable; a bottomed cylindrical-shaped firstcrucible disposed within the outer vessel; a second crucible having acommunicating opening with the first crucible at a bottom in a state ofbeing disposed within the first crucible; a crystal pulling-up shafthaving a seed crystal holding part at an end thereof; and a plate-likemember which has a pass-through slot for being capable of introducingthe crystal pulling-up shaft into the second crucible and whichfunctions as a cover of the second crucible; wherein the plate-likemember is previously inserted into the crystal pulling-up shaft; and aslipping-off preventing member for preventing the plate-like member fromslipping off is provided on the crystal pulling-up shaft.
 4. (cancelled)5. The crystal growth apparatus as claimed in claim 3, wherein theplate-like member is a quartz glass plate.
 6. The crystal growthapparatus as claimed in claim 3, wherein a difference between a diameterof the pass-through slot provided on the plate-like member and adiameter of the crystal pulling-up shaft is 1 mm or less.
 7. The crystalgrowth apparatus as claimed in claim 5, wherein a difference between adiameter of the pass-through slot provided on the plate-like member anda diameter of the crystal pulling-up shaft is 1 mm or less.